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Lease lines are an example of synchronous serial communication, where one party provides the clocking

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for the communication.

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So in other words, two devices will synchronize their clocks before data transmission takes place.

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So they will align or synchronize those clocks and agree on parameters for data transfer, including

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the data interval between bits of data.

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The CSU issue or channel service unit data service unit, commonly referred to as the CSU, provides

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the clocking and is the master for the communication.

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The rate is acting as a slave and is receiving its clocking from the CSU.

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So essentially before communication can start, the two devices have to align their clocks or agree

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on the clock intervals to ensure that data doesn't get corrupted.

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So here we have the terms data, communication equipment or DCE and data terminal equipment or DTD.

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The most in the communication is the CSU DSU and it's using its own internal clocking.

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But the rudder, which is the data terminal equipment or dty, uses the external clocking received from

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the DCE and will thus synchronize itself to the CSU DSU.

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So the CSU DSU is the DCI side of the connection and the router is the dty side of the connection.

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So the DCI, which is the CSU DSU is providing clocking to the rudder, which is the DTY, and the DCE

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also terminates the connection from the carrier, and a connection is then made from the CSU DSU to

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the router.

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Some terms to understand, therefore, is customer premises, equipment or CPE.

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This is the term that telcos or service providers use to refer to equipment that resides at the customer

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site at the end of their connection.

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So once again, in this example, the CE issued issue is at the customer's site.

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The key issue, DSU, which is the DCC, is connected in this example via a V 35 cable to the router

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and is providing clocking to the router.

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So the CSU issue, which is the DCC physically controls the speed and timing at which the router serial

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interfaces can send and receive bits over the serial cable.

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You don't have the ability to configure the speed of your serial connection that is set by the CSU DSU

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and is generally set by the service provider on your behalf.

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The serial cable once again connects the CSU to the router interface.